In copending application United States Ser. No. 188,244 filed Sept. 17, 1980, there are disclosed novel block copolymers compositions comprised of acrylonitrile sequences and sequences of glutarimide units of a molecule weight of from about 10,000 to about 2,000,000 where the acrylonitrile sequences and sequences including glutarimide units are of a molecular weight of at least about 400 with the number of sequences being at least about 2 and preferably 5 and higher. The resulting block compolymers are relatively stable with regard to acids even at elected temperatures, but are reactive to basic materials.